The present invention relates to an accumulator adapted to be disposed in the fluid supply tube system of a hydraulically operated device for temporarily storing hydraulic pressure energy or absorbing hydraulic pressure pulsations or fluctuations.
Spring-loaded accumulators are widely used such as in automotive hydraulic braking systems for storing the hydraulic pressure and discharging the stored hydraulic energy when needed. The amount of the fluid pressure energy that can be stored in the spring-loaded accumulator depends partly on the resilient force of the coil spring incorporated in the accumulator.
The spring-loaded accumulator has a fluid reservoir defined by a bore and a piston held against a piston rod extending through the coil spring, the piston being movable in the bore under the bias of the spring. To allow the spring to be extended and compressed smoothly in the tubular casing of the accumulator, there is a clearance between the spring and the inner wall surface of the tubular casing. In operation, the piston rod tends to be tilted slightly by the spring which is movable through the clearance with respect to the tubular casing. Therefore, the piston pushed by the piston rod is subject to a bending moment, and, as a result, suffers a diametrically localized load tending to produce uneven wear on the piston ring disposed around the piston. The piston ring thus worn would fail to provide a sufficient sealing capability.
Examples of spring-loaded accumulators are disclosed in Japanese Laid-Open Utility Model Publications Nos. 50-137612 and 55-66203.
The tubular casing of the accumulator is generally made of aluminum for a smaller weight. Consequently, the inner wall surface of the tubular casing is highly susceptible to wear arising from frictional engagement with the spring as it extends and contracts. The worn inner wall surface of the tubular casing results in a larger clearance between itself and the spring, thus amplifying the aforesaid problem.
Some spring-loaded accumulators have a pressure switch actuatable in response to a hydraulic pressure or a stroke switch operable in response to a piston displacement for preventing a danger which would result from an increase in the stored fluid pressure beyond a prescribed level. Dangers will also be induced by a large pressure drop, however, if the fluid leaks through the worn piston ring or the piston seizes in the bore. In automobile braking systems, such a large pressure reduction or an accumulator failure is detrimental to the proper functioning of the brake. The conventional spring-loaded accumulators have had no provision for alarming such troubles of the accumulators.